1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to an improvement in prosthetic liners of the type made from gel, reinforced by a stretchable fabric, and having a distal umbrella that enables interconnection between the liner and a prosthetic device.
2. Description of the Prior Art
Gels have been used in prosthetic interfaces since the late 1980""s. However, gels are relatively weak and cannot be used for most purposes without a fabric reinforcement. Accordingly, they are almost always used in conjunction with a fabric. Even when reinforced with fabric, most gels still break down in intensive use such as long distance running.
The most suitable fabrics for reinforcing gel liners are stretchable to enable stretching of the gel liner; the inherent strength of the fabric reinforces the gel liner.
Various distal attachment means, referred to hereinafter as distal umbrellas due to their shape, have been developed to attach the distal end of a gel/fabric combination to a prosthetic device. Significantly, the prior art teaches that the distal umbrella is mounted to an external, outside surface of the fabric. In some constructions, the distal attachment means is simply glued or otherwise attached to said exterior surface. Alternatively, a threaded aluminum nut is insert molded onto an external surface of the fabric by injection molding a thermoplastic polymer over the nut and the fabric that covers the gel. This molding operation is performed after the gel has been applied to the inside surface of the fabric.
There are two primary drawbacks to liners of this type. The first drawback is that no gel pad cushion is provided at the distal end of the liner. The second shortcoming is that the strength of the attachment is only as strong as the bond between the distal umbrella and the fabric or the bond between the molded thermoplastic polymer and the fabric.
Both of these limitations are a result of the manufacturing process used to make the fabric-covered liner. In the molding operation, the fabric cover is inverted and placed over a metal mandrel. The mandrel is then introduced into a mold cavity. If injection molding is employed, the mold cavity is filled with molten thermoplastic prior to the intriction of the mandrel into the mold cavity. If compression molding or open mold injection molding is employed, the mold cavity is filled with molten thermoplastic after introduction of the mandrel into the mold cavity. A mandrel having fabric on it is then introduced into the mold. The mold is cooled until the gel solidifies; it is then opened and the gel liner is removed from the mandrel and inverted to its right side out configuration.
If the fabric-covered liner is made by a dipping process, sometimes referred to as dip molding, the mandrel covered with a fabric is dipped several times in a gel bath with the mandrel itself being cooled. The gel deposits itself onto the fabric and solidifies on said fabric. The thickness of the gel coating on the fabric is determined by the temperature of the molten gel bath, the viscosity of the gel, the number of dips, and the temperature of the mandrel.
In both techniques (molding and dipping), the last step of the manufacturing process requires turning the liner inside out so that the gel is on the inside of the liner, in contact with the residual limb. A thick pad at the distal end cannot be provided because it would prevent such inside-out turning of the liner. Nor has the art developed a way to embed the base of the distal umbrella within the gel. If the base could be embedded, such structural feature would provide an enhanced connection between the distal umbrella and the liner.
Accordingly, there is a need for a gel liner having a fabric cover and a thick pad at its distal end and for a new method of making a gel liner having a fabric cover and a thick pad of gel at its distal end. The new method should not require that the liner be turned inside-out at the end of the manufacturing process, or at any other stage thereof.
Moreover, there is a need for an improved method of securing a distal umbrella to the distal end of a liner. Specifically, there is a need for a means for attaching a distal umbrella to the inside of the fabric instead of the outside thereof. Moreover, there is a need for a method that would enable the base of a distal umbrella to be embedded within the gel.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how these needs could be fulfilled.
The long-standing but heretofore unfulfilled need for an apparatus that overcomes the limitations of the prior art is now met by a new, useful, and nonobvious invention. The invention meets the need for a new manufacturing method capable of producing a gel liner having a fabric cover and a thick, cushioned distal end. It also provides methods for improving the connection between the liner and the distal umbrella.
The present invention is a prosthetic liner made of gel where the thickness of the gel is increased at the distal end thereof and wherein fabric reinforces the distal end to reduce pistoning of the residual limb. A distal umbrella having a base and a neck is secured to the distal end of the liner to enable connection of the liner to an artificial leg that includes an artificial foot. In a first embodiment, the base of the distal umbrella is embedded within the thickened part of the gel. In a second embodiment, the base of the distal umbrella overlies an exterior surface of the gel and underlies the fabric.
The gel is a foamed or non-foamed gel composition including a block copolymer and mineral oil.
The fabric is secured to the gel near the distal end of the prosthetic liner to limit pistoning of the distal end of a residual limb during ambulation, and the distal umbrella is secured to said distal end of the prosthetic liner to facilitate connection of the liner to another prosthetic device such as an artificial leg and foot. The fabric may be secured to an exterior surface of the liner and the fabric may extend the entire longitudinal extent of the liner or just a predetermined extent thereof. Preferably, the fabric is secured to an exterior surface of the liner in the region of the distal end of the liner, extending from the distal end a distance between about three to six inches toward the proximal end of the liner.
Alternatively, the fabric may be embedded within the liner along the entire longitudinal extent thereof, or along a predetermined extent thereof. Preferably, when the fabric is embedded, it is embedded in the region of the distal end of the liner, extending from the distal end a distance between about three to six inches toward a proximal end thereof.
The preferred fabric is a nylon-lycra combination having a first, limited extensibility in a longitudinal direction and having a second, greater extensibility in a direction radial to the longitudinal direction. The preferred combination includes 85% to 95% nylon and 5% to 15% lycra. The fabric may be provided in a single layer that is stitched or adhered to the exterior surface of the gel liner. Alternatively, the fabric may be provided in a double layer, including a first and a second layer, wherein the first and second layers of fabric are joined to one another and to the gel liner by stitching or by an elastic adhesive. Moreover, the fabric may be embedded within the gel.
The distal umbrella includes a disc or umbrella-shaped base and a neck or stem that depends from the center thereof. An internally threaded central bore is formed in the stem for engagement with an externally threaded pin that forms a part of a prosthesis.
There are numerous mechanical means for attaching the distal umbrella to the gel liner, and all such means are within the scope of this invention as long as the base of the distal umbrella is embedded within the gel or attached to the interior surface of the fabric in overlying relation to the exterior surface of the gel liner. In both cases, an elongate neck of the distal umbrella extends through a suitable opening formed in the distal end of the fabric to enable attachment of a prosthetic leg to said neck.
For example, a metallic grommet member may be used to secure the peripheral edge of the fabric that surrounds said opening to the neck of the distal umbrella. Alternatively, said peripheral edge of the fabric may be bonded to a plastic grommet member by melting or by high frequency welding. The metallic or plastic grommet members have utility in the embodiment where the base of the distal umbrella is embedded in the fabric and in the embodiment where said base overlies the exterior surface of the gel and underlies the fabric.
A metallic or textile ring that encircles the stem can also be used to anchor the peripheral edge of the fabric to the neck of the distal umbrella in both the embedded and surface-mounted embodiments.
An annular groove may also be formed in the base of the distal umbrella, and the peripheral edge of the fabric that surrounds said neck opening may be positioned within said annular groove and secured thereto by crimping shut said groove in locking relation to said fabric. This particular attachment means has primary utility in the surface-mounted embodiment.
The novel liner does not require forming over a plaster model and thus eliminates the need for several time-consuming and costly operations by the prosthetist. This feature also allows the patient to be fitted in the first office visit.
The novel liner is less costly to manufacture because the manufacturing process requires only a molding operation. Savings include the cost of the fabric, and also of the cutting, sewing and placing of the fabric in the mold. The rate of rejects is also reduced as fewer manufacturing operations are involved.
In approximately 70% of the cases where a patient needs fitting with a gel liner, and where the patient has already been provided with a hard socket, the novel liner can be donned by the patient and the residual limb introduced into the existing socket and the amputee will report a better fit than with the original liner, due to the superior conforming characteristics of the novel liner. This provides a significant economic advantage because no new hard socket is required. Moreover, the amputee is fitted within a few minutes during the first office visit.
Since the novel liner avoids the need for modification of an existing hard socket, in most cases, the prosthetist simply needs to take a negative cast of the residual limb with the novel liner on, make a positive plaster model from it, and from the positive model make the hard socket without making modifications to the positive plaster model.
The primary object of this invention is to advance the art of fabric-covered gel liners.
Another broad object is to advance the art of making fabric-covered gel liners having distal ends where the gel is thickened for cushioning purposes.
A more specific object is to advance the art of attaching distal umbrellas to the distal end of fabric-covered gel liners.
Another important object is to provide a fabric-covered gel liner having a distal umbrella where the base of the distal umbrella is embedded within the gel at the distal end of the gel liner.
Another object is to provide a fabric-covered gel liner having a distal umbrella where the base of the distal umbrella is attached to the interior side of the fabric that covers the gel liner.
These and other important objects, features, and advantages of the invention will become apparent as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.